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Staley B.F.,Environmental Research and Education Foundation | de Los Reyes F.L.,North Carolina State University | Barlaz M.A.,North Carolina State University
FEMS Microbiology Ecology | Year: 2012

Refuse decomposition in landfills is a microbially mediated process that occurs primarily under anaerobic conditions. Because of limited moisture conditions, hydraulic transport as a means of cellular translocation within the landfill appears limited, especially during the initial stages of decomposition. Thus, microbial communities within the incoming refuse serve as a primary source of facultative and obligate anaerobic microorganisms that initiate refuse decomposition. Fresh residential refuse was collected five times over 26 months, and microbial communities in these samples were compared with those in individual refuse components and decomposed refuse. Bacterial and archaeal community structures were determined using T-RFLP. The Bacterial microbial community richness was correlated (r 2 = 0.91) with seasonal differences in ambient air temperature. Analysis of the results shows that fresh refuse is most likely not the source of methanogens in landfills. Microbial communities in the solid and leachate phases were different, indicating that both matrices must be considered when characterizing microbial diversity within a landfill. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. Source


Staley B.F.,Environmental Research and Education Foundation | de los Reyes F.L.,North Carolina State University | Barlaz M.A.,North Carolina State University
Applied and Environmental Microbiology | Year: 2011

The initiation of methanogenesis in refuse occurs under high volatile fatty acid (VFA) concentration and low pH (5.5 to 6.25), which generally are reported to inhibit methanogenic Archaea. One hypothesized mechanism for the initiation of methanogenesis in refuse decomposition is the presence of pH-neutral niches within the refuse that act as methanogenesis initiation centers. To provide experimental support for this mechanism, laboratory-scale landfill reactors were operated and destructively sampled when methanogenesis initiation was observed. The active bacterial and archaeal populations were evaluated using RNA clone libraries, RNA terminal restriction fragment length polymorphism (T-RFLP), and reverse transcription-quantitative PCR (RT-qPCR). Measurements from 81 core samples from vertical and horizontal sections of each reactor showed large spatial differences in refuse pH, moisture content, and VFA concentrations. No pH-neutral niches were observed prior to methanogenesis. RNA clone library results showed that active bacterial populations belonged mostly to Clostridiales, and that methanogenic Archaea activity at low pH was attributable to Methanosarcina barkeri. After methanogenesis began, pH-neutral conditions developed in high-moisture-content areas containing substantial populations of M. barkeri. These areas expanded with increasing methane production, forming a reaction front that advanced to low-pH areas. Despite low-pH conditions in >50% of the samples within the reactors, the leachate pH was neutral, indicating that it is not an accurate indicator of landfill microbial conditions. In the absence of pH-neutral niches, this study suggests that methanogens tolerant to low pH, such as M. barkeri, are required to overcome the low-pH, high-VFA conditions present during the anaerobic acid phase of refuse decomposition. © 2011, American Society for Microbiology. Source


Gibbons R.D.,University of Chicago | Morris J.W.F.,Geosyntec Consultants | Prucha C.P.,Groundwater Protection Program | Caldwell M.D.,Groundwater Protection Program | Staley B.F.,Environmental Research and Education Foundation
Waste Management | Year: 2014

Landfill functional stability provides a target that supports no environmental threat at the relevant point of exposure in the absence of active control systems. With respect to leachate management, this study investigates "gateway" indicators for functional stability in terms of the predictability of leachate characteristics, and thus potential threat to water quality posed by leachate emissions. Historical studies conducted on changes in municipal solid waste (MSW) leachate concentrations over time (longitudinal analysis) have concentrated on indicator compounds, primarily chemical oxygen demand (COD) and biochemical oxygen demand (BOD). However, validation of these studies using an expanded database and larger constituent sets has not been performed. This study evaluated leachate data using a mixed-effects regression model to determine the extent to which leachate constituent degradation can be predicted based on waste age or operational practices. The final dataset analyzed consisted of a total of 1402 samples from 101. MSW landfills. Results from the study indicated that all leachate constituents exhibit a decreasing trend with time in the post-closure period, with 16 of the 25 target analytes and aggregate classes exhibiting a statistically significant trend consistent with well-studied indicators such as BOD. Decreasing trends in BOD concentration after landfill closure can thus be considered representative of trends for many leachate constituents of concern. © 2014 Elsevier Ltd. Source


Staley B.F.,Environmental Research and Education Foundation | Saikaly P.E.,American University of Beirut | de los Reyes III F.L.,North Carolina State University | Barlaz M.A.,North Carolina State University
Biodegradation | Year: 2011

Landfills represent a unique microbial ecosystem and play a significant role in global biogeochemical processes. The study of complex ecosystems such as landfills using DNA-based techniques can be advantageous since they allow for analysis of uncultured organisms and offer higher resolution in measuring demographic and metabolic (functional) diversity. However, sample acquisition and processing from refuse is challenging due to material heterogeneity. Decomposed refuse was used to evaluate the effect of seven sample processing methods on Bacteria and Archaea community structure using T-RFLP. Bias was assessed using measured richness and by comparing community structure using multi-dimensional scaling (MDS). Generally, direct methods were found to be most biased while indirect methods (i. e., removal of cellular material from the refuse matrix before DNA extraction) were least biased. An indirect method using PO4 buffer gave consistently high bacterial and archaeal richness and also resulted in 28 and 34% recovery of R. albus and M. formicicum spiked into refuse, respectively. However, the highest recovery of less abundant T-RFs was achieved using multiple processing methods. Results indicate differences in measured T-RF diversity from studies of landfill ecosystems could be caused by methodological (i. e., processing method) variation rather than refuse heterogeneity or true divergence in community structure. © 2010 Springer Science+Business Media B.V. Source

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